[Spectroscopic and Molecular Characterization of Water Soluble Organic Matter from Sediments in the Macrophyte-dominated and Algae-dominated Zones of Taihu Lake].

Macrophyte- and algae-dominated lakes (zones) are the two typical states of shallow lakes, where the source and composition of organic matter are distinct. The burial of organic matter (OM) in the sediment supports the role of lakes as carbon sinks. However, organic matter in the sediments could be further processed, influencing the carbon cycle. The post-burial metabolism of the sedimentary OM relates closely to its composition. However, information on the differences in composition remains limited, especially the molecular composition of organic matter from sediments in the macrophyte-dominated and algae-dominated lakes. In this study, sediments were collected from the macrophyte-dominated and algae-dominated zones of Taihu Lake (East Taihu Lake and Meiliang Bay, respectively), and the active pool of sedimentary OM (water soluble organic matter, WSOM) was extracted and purified. The composition of the WSOM was characterized in detail via absorption spectroscopy, fluorescent spectroscopy, infrared spectroscopy, and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). The optical index of E2:E3 showed that the molecular size of WSOM in the macrophyte-dominated zone (M-WSOM) was slightly larger than that in the algae-dominated zone (A-WSOM). Consistently, the intensity-weighted molecular weights were identified as 388.9 and 379.9, respectively, via FT-ICR MS analysis. M-WSOM was more humified than A-WSOM, as evidenced by the SUVA254 and HIX values. The FT-ICR MS results showed that the relative abundance of the condensed aromatic substance and the aromatics were 6.3% (intensity-weighted) and 7.7% for M-WSOM and 1.1% and 4.4% for A-WSOM, respectively. The excitation-emission matrix fluorescence-parallel factor analysis (EEM-PARAFAC) suggested that the protein-like component was more in A-WSOM than that in M-WSOM, and the FT-ICR MS results showed that the intensity-weighted relative abundances of peptides were 35.6% and 15.6% for A-WSOM and M-WSOM, respectively. The FT-ICR MS results further showed that the heteroatom-containing molecules were abundant in the sedimentary WSOM, i.e., 82.9% and 91.7% for M-WSOM and A-WSOM, respectively. The nitrogen-containing molecules dominated, contributing to 53.5% and 78.5% of M-WSOM and A-WSOM, respectively. There were 30.4% and 41.4% phosphorus-containing molecules in M-WSOM and A-WSOM, respectively. The phosphorus-containing molecules in M-WSOM were mainly aliphatics and highly unsaturated structures with low oxygen, whereas those in A-WSOM were mainly peptides. This study elucidated the detailed molecular composition of WSOM in the macrophyte-dominated and algae-dominated zones of Taihu Lake, which aids understanding of the carbon, nitrogen, and phosphorus biogeochemical cycles in lakes.

[Biodegradation of Algae-derived Organic Matter (I-DOM) from Lake Taihu].

A large amount of intracellular dissolved organic matter (I-DOM) is released during the senescent phase of phytoplankton cultures. This research investigated the bio-incubation of I-DOM of cyanobacteria in Lake Taihu under various temperatures (20, 25, and 30℃) and I-DOM initial concentrations (5, 10, and 20 mg·L-1) with the aid of ultraviolet-visible spectroscopy (UV-Vis) and three-dimensional fluorescence matrix-parallel factor (EEM-PARAFAC). I-DOM was effectively degraded during the incubation. After 14 days, the DOC removal ratio was 50% ~74%. A tryptophan-like component (C1), a ubiquitous humic-like component (C2), and two microbially-derived humic-like components (C3 and C4) contributed 80.0%, 16.0%, 3.7%, and 0.3% to the initial I-DOM, respectively. During the bio-degradation, these components are not only consumed but also produced. C1 decreased during the incubation, while C3 and C4 increased at the beginning of biodegradation and then decreased. The change trend of C2 was complicated, i.e., it decreased firstly and then increased, but decreased again after 7 days. The changes in the optical indices of Sr, E2:E3 and HIX revealed that the molecular weight of DOM increased, and the aromaticity was enhanced during degradation. The reaction temperature and the initial concentration of I-DOM did not change the trend of the PARAFAC components. The temperature of 25℃ was the most suitable for I-DOM bio-degradation. Additionally, the degradation of I-DOM was enhanced with the increase in the initial concentration of I-DOM. Combined with our study on the photodegradation of I-DOM, the possible fate of I-DOM in Lake Taihu was proposed. The tryptophan-like compound could be effectively degraded, while the humic-like components could not be degraded completely. These humic-like components would potentially settle through adsorption or coprecipitation with metal substances. These results are helpful to understand the fate of I-DOM released by a cyanobacteria bloom in Lake Taihu.

[Study on the degradation of atrazine in photo-Fenton-like system under visible light irradiation promoted by N-doped Ta2O5].

In this study, N-doped Ta2O5 samples which have strong absorption in visible domain, were prepared by the nitridation of Ta2O5 under NH4 flow and then added into photo-Fenton-like system to enhance Fe3+ reduction and atrazine degradation under visible light irradiation. The sample prepared at 700 degrees C under a NH3 flow rate of 0.3 L x min(-1) for 6 h showed the highest level of photocatalytic activity for Fe3+ reduction. The influence of various operational parameters such as the light intensity, input of N-doped Ta2O5, pH and initial concentrations of Fe3+, H2O2 and atrazine were investigated. And the changesof H2O2 during the degradation were measured to explain the effect of the operational parameters. The degradation ratio of atrazine reached 97% after 60 min irradiation by 500 W Xe lamp under the conditions of pH = 2.6, [atrazine]0 = 18 mg x L(-1), [H2O2]0 = 2.5 mmol x L(-1), [Fe3+]0 = 0.5 mmol x L(-1) and the input of N-doped Ta2O5 = 0.6 g x L(-1).